// Tencent is pleased to support the open source community by making RapidJSON available.
//
// Copyright (C) 2015 THL A29 Limited, a Tencent company, and Milo Yip. All rights reserved.
//
// Licensed under the MIT License (the "License"); you may not use this file except
// in compliance with the License. You may obtain a copy of the License at
//
// http://opensource.org/licenses/MIT
//
// Unless required by applicable law or agreed to in writing, software distributed
// under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
// CONDITIONS OF ANY KIND, either express or implied. See the License for the
// specific language governing permissions and limitations under the License.

// This is a C++ header-only implementation of Grisu2 algorithm from the publication:
// Loitsch, Florian. "Printing floating-point numbers quickly and accurately with
// integers." ACM Sigplan Notices 45.6 (2010): 233-243.

#ifndef RAPIDJSON_DTOA_
#define RAPIDJSON_DTOA_

#include "itoa.h" // GetDigitsLut()
#include "diyfp.h"
#include "ieee754.h"

RAPIDJSON_NAMESPACE_BEGIN
namespace internal {

#ifdef __GNUC__
RAPIDJSON_DIAG_PUSH
RAPIDJSON_DIAG_OFF(effc++)
RAPIDJSON_DIAG_OFF(
    array - bounds) // some gcc versions generate wrong warnings https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59124
#endif

inline void GrisuRound(char* buffer, int len, uint64_t delta, uint64_t rest, uint64_t ten_kappa, uint64_t wp_w) {
	while (rest < wp_w && delta - rest >= ten_kappa &&
	       (rest + ten_kappa < wp_w || /// closer
	        wp_w - rest > rest + ten_kappa - wp_w)) {
		buffer[len - 1]--;
		rest += ten_kappa;
	}
}

inline unsigned CountDecimalDigit32(uint32_t n) {
	// Simple pure C++ implementation was faster than __builtin_clz version in this situation.
	if (n < 10)
		return 1;
	if (n < 100)
		return 2;
	if (n < 1000)
		return 3;
	if (n < 10000)
		return 4;
	if (n < 100000)
		return 5;
	if (n < 1000000)
		return 6;
	if (n < 10000000)
		return 7;
	if (n < 100000000)
		return 8;
	// Will not reach 10 digits in DigitGen()
	// if (n < 1000000000) return 9;
	// return 10;
	return 9;
}

inline void DigitGen(const DiyFp& W, const DiyFp& Mp, uint64_t delta, char* buffer, int* len, int* K) {
	static const uint32_t kPow10[] = { 1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000 };
	const DiyFp one(uint64_t(1) << -Mp.e, Mp.e);
	const DiyFp wp_w = Mp - W;
	uint32_t p1 = static_cast<uint32_t>(Mp.f >> -one.e);
	uint64_t p2 = Mp.f & (one.f - 1);
	unsigned kappa = CountDecimalDigit32(p1); // kappa in [0, 9]
	*len = 0;

	while (kappa > 0) {
		uint32_t d = 0;
		switch (kappa) {
		case 9:
			d = p1 / 100000000;
			p1 %= 100000000;
			break;
		case 8:
			d = p1 / 10000000;
			p1 %= 10000000;
			break;
		case 7:
			d = p1 / 1000000;
			p1 %= 1000000;
			break;
		case 6:
			d = p1 / 100000;
			p1 %= 100000;
			break;
		case 5:
			d = p1 / 10000;
			p1 %= 10000;
			break;
		case 4:
			d = p1 / 1000;
			p1 %= 1000;
			break;
		case 3:
			d = p1 / 100;
			p1 %= 100;
			break;
		case 2:
			d = p1 / 10;
			p1 %= 10;
			break;
		case 1:
			d = p1;
			p1 = 0;
			break;
		default:;
		}
		if (d || *len)
			buffer[(*len)++] = static_cast<char>('0' + static_cast<char>(d));
		kappa--;
		uint64_t tmp = (static_cast<uint64_t>(p1) << -one.e) + p2;
		if (tmp <= delta) {
			*K += kappa;
			GrisuRound(buffer, *len, delta, tmp, static_cast<uint64_t>(kPow10[kappa]) << -one.e, wp_w.f);
			return;
		}
	}

	// kappa = 0
	for (;;) {
		p2 *= 10;
		delta *= 10;
		char d = static_cast<char>(p2 >> -one.e);
		if (d || *len)
			buffer[(*len)++] = static_cast<char>('0' + d);
		p2 &= one.f - 1;
		kappa--;
		if (p2 < delta) {
			*K += kappa;
			int index = -static_cast<int>(kappa);
			GrisuRound(buffer, *len, delta, p2, one.f, wp_w.f * (index < 9 ? kPow10[-static_cast<int>(kappa)] : 0));
			return;
		}
	}
}

inline void Grisu2(double value, char* buffer, int* length, int* K) {
	const DiyFp v(value);
	DiyFp w_m, w_p;
	v.NormalizedBoundaries(&w_m, &w_p);

	const DiyFp c_mk = GetCachedPower(w_p.e, K);
	const DiyFp W = v.Normalize() * c_mk;
	DiyFp Wp = w_p * c_mk;
	DiyFp Wm = w_m * c_mk;
	Wm.f++;
	Wp.f--;
	DigitGen(W, Wp, Wp.f - Wm.f, buffer, length, K);
}

inline char* WriteExponent(int K, char* buffer) {
	if (K < 0) {
		*buffer++ = '-';
		K = -K;
	}

	if (K >= 100) {
		*buffer++ = static_cast<char>('0' + static_cast<char>(K / 100));
		K %= 100;
		const char* d = GetDigitsLut() + K * 2;
		*buffer++ = d[0];
		*buffer++ = d[1];
	} else if (K >= 10) {
		const char* d = GetDigitsLut() + K * 2;
		*buffer++ = d[0];
		*buffer++ = d[1];
	} else
		*buffer++ = static_cast<char>('0' + static_cast<char>(K));

	return buffer;
}

inline char* Prettify(char* buffer, int length, int k, int maxDecimalPlaces) {
	const int kk = length + k; // 10^(kk-1) <= v < 10^kk

	if (0 <= k && kk <= 21) {
		// 1234e7 -> 12340000000
		for (int i = length; i < kk; i++)
			buffer[i] = '0';
		buffer[kk] = '.';
		buffer[kk + 1] = '0';
		return &buffer[kk + 2];
	} else if (0 < kk && kk <= 21) {
		// 1234e-2 -> 12.34
		std::memmove(&buffer[kk + 1], &buffer[kk], static_cast<size_t>(length - kk));
		buffer[kk] = '.';
		if (0 > k + maxDecimalPlaces) {
			// When maxDecimalPlaces = 2, 1.2345 -> 1.23, 1.102 -> 1.1
			// Remove extra trailing zeros (at least one) after truncation.
			for (int i = kk + maxDecimalPlaces; i > kk + 1; i--)
				if (buffer[i] != '0')
					return &buffer[i + 1];
			return &buffer[kk + 2]; // Reserve one zero
		} else
			return &buffer[length + 1];
	} else if (-6 < kk && kk <= 0) {
		// 1234e-6 -> 0.001234
		const int offset = 2 - kk;
		std::memmove(&buffer[offset], &buffer[0], static_cast<size_t>(length));
		buffer[0] = '0';
		buffer[1] = '.';
		for (int i = 2; i < offset; i++)
			buffer[i] = '0';
		if (length - kk > maxDecimalPlaces) {
			// When maxDecimalPlaces = 2, 0.123 -> 0.12, 0.102 -> 0.1
			// Remove extra trailing zeros (at least one) after truncation.
			for (int i = maxDecimalPlaces + 1; i > 2; i--)
				if (buffer[i] != '0')
					return &buffer[i + 1];
			return &buffer[3]; // Reserve one zero
		} else
			return &buffer[length + offset];
	} else if (kk < -maxDecimalPlaces) {
		// Truncate to zero
		buffer[0] = '0';
		buffer[1] = '.';
		buffer[2] = '0';
		return &buffer[3];
	} else if (length == 1) {
		// 1e30
		buffer[1] = 'e';
		return WriteExponent(kk - 1, &buffer[2]);
	} else {
		// 1234e30 -> 1.234e33
		std::memmove(&buffer[2], &buffer[1], static_cast<size_t>(length - 1));
		buffer[1] = '.';
		buffer[length + 1] = 'e';
		return WriteExponent(kk - 1, &buffer[0 + length + 2]);
	}
}

inline char* dtoa(double value, char* buffer, int maxDecimalPlaces = 324) {
	RAPIDJSON_ASSERT(maxDecimalPlaces >= 1);
	Double d(value);
	if (d.IsZero()) {
		if (d.Sign())
			*buffer++ = '-'; // -0.0, Issue #289
		buffer[0] = '0';
		buffer[1] = '.';
		buffer[2] = '0';
		return &buffer[3];
	} else {
		if (value < 0) {
			*buffer++ = '-';
			value = -value;
		}
		int length, K;
		Grisu2(value, buffer, &length, &K);
		return Prettify(buffer, length, K, maxDecimalPlaces);
	}
}

#ifdef __GNUC__
RAPIDJSON_DIAG_POP
#endif

} // namespace internal
RAPIDJSON_NAMESPACE_END

#endif // RAPIDJSON_DTOA_
